Movie Lesson No. 1,287: When P. Diddy chases you, you run. Because he'll mindf*ck the sh*t out of you, motherf*cker.

As much as affection as everyone felt for Jason Segel’s Peter, the dumped schlub in “Forgetting Sarah Marshall,” there was no denying the real star was Russell Brand. The coiffure that suggests mental illness, the sexual pyrotechnics, that explosive Jack Sparrow/Freddie Mercury persona — Brand’s media whore Aldous Snow was the chap we couldn’t take our eyes off of. Powerless we were (or me were) to that rakish, nimble Brit wit; indeed, a rock star who blows off a stalker with “I was going to, but then I just carried on living my life” has formidable powers of observation.

As it happens, the “stalker” in question (same actor, different character) makes an appearance in Nicholas Stoller’s dirty-minded and raucous “Get Him to the Greek,” an exploration of the character Segel created two years ago. This time around, though, Jonah Hill, blank-eyed straight man to Russell Brand’s alcoholic snatch bandit, has flattened out the weirder edges of his character and made him a genuine fan sans “Single White Female” undertones. Hill, like his “Superbad” bud Michael Cera, has two speeds: crazed rants or deadpan observations. Because he does both well, he’s an excellent foil for Brand, who rushes into every experience with all the zeal of a bull after a cape-waving matador. The odd couple angle is old as time immemorial, but when the chemistry’s clicking it works like a beaut. Brand and Hill are two funnymen — both smarter than they look or act — who can sell this story.

“Get Him to the Greek” finds Aldous Snow in a different place than “Forgetting Sarah Marshall” did. His career has taken a nosedive thanks to a godawful single called “African Child.” If the song is a disaster, the video is on par with the BP oil spill, painting Aldous as a white rock star Jesus Christ. His relationship with inane British pop star Jackie Q (Rose Byrne, cheerfully tarty) has soured, so Aldous, former poster child for sobriety, hops back on the sauce. Every sauce. Fan Aaron Green (Hill), an intern at Pinnacle Records living with his girlfriend Daphne (Elizabeth Moss), devises a plan to put “the last real rock star” on top: a live concert at L.A.’s Greek Theatre to commemorate the last show Aldous played there. His ball-busting boss Sergio (Sean “P. Diddy” Combs, who apparently has a personality and, like, jokes) charges him with collecting Aldous from London, getting him to The Today Show and delivering him to the Greek Theatre. In actual world, this scenario would end in a series of shouting matches and a drug overdose, but in movie world it’s a yellow brick road to Hijinksville.

Critical to the success of this orchestrated hilary is the feeling of spontaneity and the rapport between the buddies in question. We expect certain shenanigans — clubbing, sexcapades — and then the film throws some wild cards (to say nothing of the brawl involving a “Geoffrey,” P. Diddy going medieval/mindfucking/cementing a new career dedicated to funny cameos and “stroking the furry wall,” which is not a euphemism). Every situation is funny. Brand and Hill’s reactions to situations are funny. And not since “The Odd Couple” has there been a wedding of two less similar people. Brand specializes in shoving people outside their comfort zones — he bathed with a homeless junkie on his U.K. show — while Hill specializes in looking fetchingly uncomfortable outside his box. They’re a formidable duo because Hill’s flair for understatement (only he could make a line like “I think I was raped” that funny) balances Brand’s childlike antics. Each actor gives a touch of humanity, especially Brand. There’s a moment where Aldous, seeking his deadbeat dad’s (Colm Meaney) approval, has such a wounded look about the peepers that the reasons for his behavior are painfully clear. Aaron takes notice, sympathizes in such a way that we understand how these two might become friends: They fill gaps*. You may say that’s too deep for a movie about a singer who writes a song about gonorrhea, but anything jives when Brand’s on the set.